Hello Kin,
Not an ideal approach to use the migration functionality to upload the fixed assets in the system. but this is the only way you could upload the fixed asset to the Bydesign system.
Also Could you check :
1) Help center document : Posting Assets Under Construction
2) SCN thread :
Asset under construction without project management
If that suits your requirement.
Mark this thread as answered, If this answers your concerns.
Let me know if you need further help/clarifications.
Regards,
Harshal Vakil